问题:Java 中参数的传递是以什么方式传递的?
回答:
- Java中参数类型传递都是值传递
- 基本数据类型的值传递采用先对值进行拷贝再传递
- 对象类型的值传递传递的是对象的地址
- String 虽然是对象类型,但是它的参数传递方式和基本数据类型相同
1. 基本数据类型先对值进行拷贝再传递
public class ParameterPassingTest {
public void function1(int a){
a = 10;
}
public void function2(Dog dog){
dog.setName("paul");
}
public void function3(String str){
str = "changed";
}
}
调用 function1() 查看当为基本数据类型的引用赋值时的变化:
System.out.println("++++++++++++++++++++");
System.out.println("a:" + a);
passing.function1(1);
System.out.println("a:" + a);
System.out.println("++++++++++++++++++++");
++++++++++++++++++++
a:11
a:11
++++++++++++++++++++
a 的值不变,说明对基本类型的引用赋值不改变原来的值
2. 对象类型传递对象的地址
public class Dog {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
调用 function2() 查看当为对象类型的引用赋值时的变化:
System.out.println("++++++++++++++++++++");
Dog dog = new Dog();
dog.setName("Mike");
System.out.println("Dog:" + dog.getName());
passing.function2(dog);
System.out.println("Dog:" + dog.getName());
System.out.println("++++++++++++++++++++");
++++++++++++++++++++
Dog:Mike
Dog:paul
++++++++++++++++++++
name 改变:说明引用拿到了对象的地址,并通过地址对其值直接进行修改
3. String 类型是特例
System.out.println("++++++++++++++++++++");
String str = "abc";
System.out.println("str:" + str);
passing.function3(str);
System.out.println("str:" + str);
System.out.println("++++++++++++++++++++");
“`
++++++++++++++++++++
str:abc
str:abc
++++++++++++++++++++
““
String 虽然是对象类型,但是其值传递结果和基本数据类型一样。